In an image reading apparatus used in digital copiers, in order to read an image for one line extending in a main scanning direction, a light source illuminates an original document with light in a line form extending in the main scanning direction and the light reflected from the original document is collected by a lens so as to be incident onto an image sensor.
When an image reading region of the original document is illuminated by illumination light from only one direction, there is a concern that illumination irregularity of the illumination light may occur.